Substract last N values from rle() object

Question

The following function is used to create a path overview for the following dataset:

tc <- textConnection('
path           touchpoint  time
abc             A           1        
abc             A           2        
abc             B           3        
abc             C           4         
def             A           2       
def             B           3       
def             D           4        
def             C           5        
def             D           6 
ghi             A           1
ghi             A           2
ghi             A           3
ghi             C           4
jkl             A           5        
jkl             A           6        
jkl             B           7        
jkl             C           8     
mno             B           1        
mno             A           2        
mno             A           3       
mno             C           4 
pqr             A           1
pqr             C           2
')

paths <- read.table(tc, header=TRUE)

--

library(plyr)

foo <- function(x){
  r <- rle(as.character(x))
  short <- paste0(r$values, collapse="_")
  long  <- paste0(r$values, "(", r$lengths, ")", collapse="_")
  data.frame(short, long)
}

ddply(paths, .(path), function(x)foo(x$touchpoint))

  path                     short                            long
1  abc                     A_B_C                  A(2)_B(1)_C(1)
2  def                 A_B_D_C_D        A(1)_B(1)_D(1)_C(1)_D(1)
3  ghi                       A_C                       A(3)_C(1)
4  jkl                     A_B_C                  A(2)_B(1)_C(1)
5  mno                     B_A_C                  B(1)_A(2)_C(1)
6  pqr                       A_C                       A(1)_C(1)

Thus this function creates two forms of 'paths':

Short provides the sequence of touchpoints per path from least recent to most recent.
Long provides the sequence of touchpoints per path from least recent to most recent including the number of times a touchpoint was involved.

Since the number of touchpoints can be quite large for some paths, I would like to incorporate the following constraint: only select the n most recent values from short and long. Since the paths are constructed from an rle() object, my question is:

How can I get N values and their corresponding lengths from an rle() object? Since the paths are saved from least recent touchpoint to most recent touchpoint, the last N values and corresponding lengths need to be selected. rle() documentation does not provide a solution for this issue.

Expected outcome if N=2 will be:

  path                     short                            long
1  abc                     B_C                          B(1)_C(1)
2  def                     C_D                          C(1)_D(1)
3  ghi                     A_C                          A(3)_C(1)
4  jkl                     B_C                          B(1)_C(1)
5  mno                     A_C                          A(2)_C(1)
6  pqr                     A_C                          A(1)_C(1)

Jouni Helske · Accepted Answer · 2013-03-11T12:16:29.293

6

Take only the last N values from r$values and r$lengths:

foo <- function(x,N){
  r <- rle(as.character(x))
  lastN<-max(1,(length(r$lengths) - N + 1)):length(r$lengths)
  short <- paste0(r$values[lastN], collapse="_")
  long  <- paste0(r$values[lastN], "(", r$lengths[lastN], ")", collapse="_")
  data.frame(short, long)
}


ddply(paths, .(path), function(x) foo(x$touchpoint,N=2))

  path short      long
1  abc   B_C B(1)_C(1)
2  def   C_D C(1)_D(1)
3  ghi   A_C A(3)_C(1)
4  jkl   B_C B(1)_C(1)
5  mno   A_C A(2)_C(1)
6  pqr   A_C A(1)_C(1)

 ddply(paths, .(path), function(x) foo(x$touchpoint,N=4))
  path   short                long
1  abc   A_B_C      A(2)_B(1)_C(1)
2  def B_D_C_D B(1)_D(1)_C(1)_D(1)
3  ghi     A_C           A(3)_C(1)
4  jkl   A_B_C      A(2)_B(1)_C(1)
5  mno   B_A_C      B(1)_A(2)_C(1)
6  pqr     A_C           A(1)_C(1)

EDIT: Edited the function to take last N values, not the first.

edited Mar 11 '13 at 12:16

answered Mar 11 '13 at 11:08

Jouni Helske

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2

OP wants the last N values, not the first N. – juba Mar 11 '13 at 11:10
OK, that was easier then expected. I was struggling with getting values from the `rle()` object, but this is cool and works perfectly! Thanks! – Max van der Heijden Mar 11 '13 at 11:18
This doesn't work if N > the length of the selected row. For instance if I set N=4, i get: `only 0's may be mixed with negative subscripts` – Max van der Heijden Mar 11 '13 at 11:43
@MaxvanderHeijden Good point, I edited the function (line `lastN<-max(1,(length(r$lengths) - N + 1)):length(r$lengths)`), now in case the length is less than N, function returns all values. – Jouni Helske Mar 11 '13 at 11:47

Substract last N values from rle() object

1 Answers1